fastobo: add build-fastobo.yml for riscv64 wheels

[luhenry]

• Package: fastobo
• Version: 0.14.1
• Source: https://github.com/fastobo/fastobo-py/
• Docs: https://github.com/fastobo/fastobo-py/

Compiles the fastobo-py PyO3/maturin extension, a Rust binding around the fastobo crate for parsing and validating OBO (Open Biomedical Ontologies) format files. Upstream publishes no riscv64 wheel.

Mirrors the wheel-linux-x86_64 job of upstream's publish.yml; upstream's own pyproject.toml already installs rustup and sets PATH for the Linux build, so the workflow only adds riscv64 selection.

Differs from upstream

• musllinux dropped - rustup.rs ships no riscv64 musl toolchain, the usual constraint for Rust extensions here.

Testing

• same as upstream

License: OK

Verified locally against the published PyPI wheel: python -m unittest discover -s . -v from the v0.14.1 checkout, 189 tests ran, OK (3 expected failures). cargo check --features extension-module also compiles cleanly.